Existing Pneumatic Solid Waste Collection Systems (PSWCS) convey solid waste by air movement from several intermediate holding areas (IHA) which are fed by indoor gravity chutes or outdoor throw stations to a central collection point called the Refuse Collection Station (RCS) by a network of surface and underground pipes and air valves. The solid waste which is temporarily stored in a plug is broken up by an air stream to move the solid waste in a rare or dispersed phase allowing for the solid waste to move in smaller dispersed parts.
The RCS itself is a self-contained facility combining major components of refuse separator(s), compactor(s), container(s), vacuum equipment, compressed air system, filtration system(s), deodorising system(s), valves, pipes, control system and electrical power supply panel.
In large developments there would be several self-contained RCS each covering a section of the development. The limitation of the system is the maximum conveying distance of the solid waste between the furthest IHA and the RCS which is about 2.5 kilometers, after which the system becomes extremely inefficient in terms of energy efficiency.
Whilst the concept of PSWCS is readily accepted by most building owners and managers alike, the greatest obstacles remain high investment cost, lack of space within the development and maintenance of specialised equipment in such a facility that has to be undertaken by skilled technicians.
The existing method that is adopted to minimise space and upfront capital expenditure is by using multiple temporary storage compartments at base of collection chutes connected to a fixed solid waste collection conduit that terminates at one or more docking stations to which a mobile vacuum truck periodically affixes a hose to suck the solid waste from the temporary storage compartments. Whilst capital expenditure to this development is lower in absence of permanent plant room, vacuum truck service has to be frequent, is expensive, very noisy during collection mode and very limited in service vendors due to major capital expenditure of the vacuum trucks. A further problem is that as vacuum plant is now mounted on the vacuum truck which makes the vacuum truck very heavy. Furthermore, dead weight of the vacuum truck makes it extremely wasteful in terms of fuel consumption and very high on maintenance costs. In short the capital expenditure to developer is reduced but operating life cycle costs to the development is very high and dependent on a limited vendor source.
Conventionally designed PSWCS use pipes that generally vary in diameter from 400 mm to 500 mm although in exceptional cases where very long solid waste transfer distances are required, the pipes can reach up to 600 mm diameter. General principle for conventional design is to have one size diameter of waste transport conduit for the entire PSWCS. Problem using the 600 mm diameter pipe for conveying of the solid waste is that sub-atmospheric pressures to generate huge quantities of air movement is needed to be generated by vacuum equipment to maintain minimum air speed in the pipes required for conveying the waste. This translates to use of very costly and high powered vacuum equipment to generate sub-atmospheric pressures to create air movement which in turn leads to high operating costs for the PSWCS.
Another shortcoming of conventional design which indirectly leads to a disproportionate higher initial investment cost is the idling of system between conveying cycles. Typically operating time of vacuum equipment in smaller developments may be no more than 90 minutes in a day.
Another problem with conventionally designed systems conveying large masses of solid waste over very long distances at high speeds is the problem of abrasion in pipes. Due to this abrasion, steel pipes have often been selected as the most suitable material. The downside of this material though has been corrosion as solid waste is often wet and generates a highly acidic liquid called leachate which attacks metals. The corrosive attack on both the internal and external surfaces of the pipe can be reduced with cathodic protection which is costly and requires regular inspection and maintenance. Generally the longer the pipe in a system the larger the area covered, the higher the solid waste load, the greater the abrasion, the thicker the pipes have to be resulting in higher capital costs.
The problem with traditional PSWCS is that smaller developments limited to one or two buildings tend to avoid investing in the system due to the high initial capital cost and large space requirement for the RCS.
The scope of the present invention is to address these concerns and to allow for a greater penetration of these useful systems into large developments and districts that may be under planning, in construction or even existing but in the process of being upgraded.